As colorless and transparent materials, various materials have been used in an optical lens, a functional optical film and a disk substrate, depending on various applications, and with rapid development in health care and electronics, functions and performance required of the materials themselves become increasingly accurate and excellent.
In application to health care, an eyeglass lens can be mentioned, and from the viewpoint of thinning, light weight and fashion, active development of materials is made, and for advantages such as impact resistance, light weight etc., resin lenses come to account for 90% of the commercial eyeglass lenses at present.
The resin for conventional eyeglass lenses is divided roughly into 3 kinds of resin, that is, CR39, acrylic resin and urethane resin, and many resins have been developed and practically used to achieve low dispersibility and high refraction. Because all of these resins are thermosetting, cast molding is used in molding thereof into optical lenses, but this method suffers from problems such as long polymerization time and high production costs in a subsequent annealing process etc. Application of thermoplastic resin such as polycarbonate to lenses is advantageous in a significant reduction in production costs with good moldability, as compared with the thermosetting resin, but the thermoplastic resin applied to eyeglasses for eyesight correction is poor in performance because of a low Abbe number (that is, high chromatic aberration due to high dispersibility) and relatively high optical strain. A large number of thermoplastic resins having a higher refractive index than that of polycarbonate are known, but have problems such as high dispersibility, easy coloration etc. and are thus problematic for use in optical lenses.
Various resins containing a phosphorus-based functional group are known, and resins containing a phosphonate group in a main chain thereof are called polyphosphonates and vigorously studied for improvement in functions such as flame retardance. With respect to many of such known polyphosphonate-based resins, there is no detailed knowledge of physical properties such as optical properties and physical properties, and thus the present inventors synthesized such resins and evaluated physical properties thereof. As a result, these known polyphosphonate-based resins are poor in physical properties or poor in refractive index and light dispersibility.
In the Patent Document 1, the optical properties etc. of a phosphonate/carbonate copolymer are described in detail, and the optical properties thereof are improved as compared with those of conventional resin. However, the light dispersibility (Abbe number) of the resin described in the patent application supra cannot be said to be satisfactory for use in optical lenses, so there is need a resin having a high refractive index and a further high Abbe number.
Patent Document 1: European Patent Application No. 1270646A1